"虚无缥缈" is formed by coupling two two-character compounds: "虚无", meaning "emptiness" or "nothingness" (from "虚" for empty and "无" for without), and "缥缈", meaning "vague and elusive" (from "缥" for faint and "缈" for distant). The combination merges these synonymous concepts to describe something illusory and insubstantial.